Nikon N70 AF Instruction Manual page 74

AUTO EXPOSURE LOCK FUNCTION WITH AE-L BUDON
In the auto exposure mode, when you want to control exposure
based on the brightness of a specific area within the scene, use
Auto Exposure Lock function. For Auto Exposure Lock
function , it is recommended that you should switch the
metering system to Center-Weighted or Spot.
1
Center main subject inside viewfinder and/or move in
closer until reference circle for Center-Weighted metering
or Spot metering is fully covered by the subject.
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2
Lightly press shutter release button, and confirm shutter
speed and aperture in viewfinder.